Nitrogen cycling in semi-arid mediterranean zones : removal and return of nitrogen to pastures by grazing sheep

The intake of nitrogen and its removal, return, and partition between urine, faeces, and milk was measured over 5 months in Awassi ewes grazing medic pasture or barley. Total faeces and urine were collected in bags carried by the ewes for 5-day collection periods at monthly intervals. Bags were changed in the morning and evening so that excreta produced in the fleld or in the yards at night were collected separately. Nitrogen was partitioned between the urine and faeces on the basis of the N : ADF ratio of samples of faeces taken directly from the rectum of the animal when the bags were changed. Outputs of excreta and N were very similar in the fleld and at night in the yard. When N output in the milk was included, 20% more N was removed from the fleld than was returned. The partitioning of N output between urine and faeces changed markedly during the season and corresponded with changes in the quality of the herbage. Fifty per cent and 65% of the removal of N in faeces and urine, respectively, occurred in the flrst 2 months of the experiment.